题目内容

(2)Read the following passage “Poetic Moments in China’s Aid in Pandemic Fight”, matching poemswith thecountries China donated to:China has been offering helping hands to other countries in the global fight against the novel coronavirus pneumonia outbreak, sometimes in a quite poetic way.Here are some of the touching poems sent along with Chinese donations to epidemic-hit areas.Great distance cannot separate us, we all live in a united world – the poem, written by Korean sholar Choe Chi-won, appears on the packaging of surgical masks donated by China to South Korea.The sons of Adam are limbs of each other, having been created of one essence – the quotation from ancient Persian poet Saadi Shirazi appears on the packaging of medicai supplies donated by China to Iran.Like the mountain range that stretches before you and me, let's share the same trials and hardships together – the words, adapted from a poem written by Tang Dynasty poet Wang Changling, appear on the packaging of masks donated by a Chinese foundation to Japan.United we shall overcome – the quote by French writer Victor Hugo appears on the packaging of medical supplies donated by China to France.We are waves of the same sea, leaves of the same tree, flowers of the same garden - the quote, by ancient Roaman philosopher Seneca, appear on the packaging of masks donated by a Chinese company to Italy.

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比例环节的相频特性为( )。

A. 0°
B. -90°
C. 90°
D. 180°

关于系统开环传递函数的幅相频率特性曲线图,说法错误的有( )。

A. 只要系统含有积分环节,奈奎斯特曲线就起始于无穷远。
B. 起始于无穷远的奈奎斯特曲线,从哪个象限开始绘制取决于转折频率最低环节的相角。
C. 奈奎斯特曲线与负实轴的交点频率称为穿越频率,可以令频率特性函数的虚部为0求出。
D. 所有奈奎斯特曲线都终止于坐标原点。

若某最小相位系统的相角裕度γ>0°,则下列说法正确的是( )。

A. 系统不稳定
B. 不能根据相角裕度判断系统稳定性
C. 系统稳定
D. 只有当幅值裕度大于1时系统才稳定

给稳定的系统输入一个正弦信号,则输出的稳态仍为正弦信号。

A. 对
B. 错

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